Field of the Invention
The present invention relates to a heating method of honeycomb structure. More particularly, it relates to a heating method of honeycomb structure in which it is possible to suitably heat the honeycomb structure with less temperature unevenness during the heating and with less power consumption.
Description of Related Art
Heretofore, honeycomb structures made of cordierite and onto which catalyst is loaded have been used in treatment of harmful substance in exhaust gas discharged from car engines. Furthermore, it is also known that honeycomb structures formed by silicon carbide sintered body are for use in purification of exhaust gas (e.g., see Patent Document 1).
When the harmful substance included in the exhaust gas is to be treated by the catalyst, it is necessary to raise a temperature of the catalyst up to a predetermined temperature. That is, for effectively developing a catalytic function of the catalyst, it is necessary to raise the temperature of the catalyst up to such a temperature as to activate the catalyst or more. However, at the start of an engine, the temperature of the catalyst is low, and hence there has been the problem that the exhaust gas is not sufficiently purified.
To solve the problem, there has been investigated a method of disposing a heater made of a metal on an upstream side of a honeycomb structure onto which a catalyst is loaded, to raise a temperature of an exhaust gas (e.g., see Patent Document 2).
Furthermore, it has been disclosed that a honeycomb structure which is made of a conductive ceramic material and in which electrodes are disposed in both end portions is used as a catalyst carrier with a heater (e.g., see Patent Document 3).
Furthermore, there has been disclosed a honeycomb structure including a tubular honeycomb structure body having porous partition walls and a circumferential wall positioned at an outermost circumference, and a pair of electrode members disposed on a side surface of the honeycomb structure body (e.g., Patent Document 4). In the honeycomb structure described in Patent Document 4, an electrical resistivity of the honeycomb structure body is from 1 to 200 Ωcm. A voltage is applied between the pair of electrode members of this honeycomb structure to supply a power to the honeycomb structure body, so that the honeycomb structure body can be heated. That is, such a honeycomb structure is a catalyst carrier which also functions as a heater, when the voltage is applied.
As described above, when the exhaust gas is treated by the catalyst loaded onto the honeycomb structure, it is necessary to raise the temperature of the catalyst up to a predetermined temperature. Therefore, when the honeycomb structure onto which the catalyst is loaded as described in Patent Document 4 is used in the treatment of the harmful substance in the exhaust gas, the temperature of the honeycomb structure body has been raised up to a temperature at which the loaded catalyst is activated or more. Hereinafter, the “temperature at which the catalyst is activated” may be referred to as “catalyst activating temperature”.